The present invention is directed to the separation of polynucleotides using non-polar separation surfaces, such as the surfaces of polymeric beads and surfaces within molded monoliths, which are substantially free from contamination with multivalent cations.
Separations of polynucleotides such as DNA have been traditionally performed using slab gel electrophoresis or capillary electrophoresis. However, liquid chromatographic separations of polynucleotides are becoming more important because of the ability to automate the analysis and to collect fractions after they have been separated. Therefore, columns for polynucleotide separation by liquid chromatography (LC) are becoming more important.
High quality materials for double stranded DNA separations previously have been based on polymeric substrates disclosed in U.S. Pat. No. 5,585,236, to Bonn, et al. (1996), which showed that double-stranded DNA can be separated on the basis of size with selectivity and performance similar to gel electrophoresis using a process characterized as reverse phase ion pairing chromatography (RPIPC). However, the chromatographic material described was limited to nonporous beads substituted with alkyl groups having at least 3 carbons because Bonn, et al. were unsuccessful in obtaining separations using polymer beads lacking this substitution. Additionally, the polymer beads were limited to a small group of vinyl aromatic monomers, and Bonn et al. were unable to effect double stranded DNA separations with other materials.
A need continues to exist for chromatographic methods for separating polynucleotides with improved separation efficiency and resolution.
Accordingly, one object of the present invention is to provide a chromatographic method for separating polynucleotides with improved separation and efficiency.
Another object of the present invention is to provide a method for separating polynucleotides using nonporous polymer separation media, such as beads or monoliths (e.g., rods), having non-reactive, non-polar surfaces.
It is another object of this invention to provide the chromatographic separation of polynucleotides using nonporous polymeric separation media made from a variety of different polymerizable monomers.
It is a further object of this invention to provide the chromatographic separation of polynucleotides using polymeric separation media which can be unsubstituted, methyl-substituted, ethyl-substituted, hydrocarbon-substituted, or hydrocarbon polymer-substituted.
Yet another object of the present invention is to provide improved polymer separation media by including steps to remove contamination occurring during the manufacturing process.
Still another object of the invention is to provide a method for separating polynucleotides using a variety of different solvent systems.
These and other objects which will become apparent from the following specification have been achieved by the present invention.
In one aspect, the invention is a method for separating a mixture of polynucleotides by applying a mixture of polynucleotides having up to 1500 base pairs to a polymeric separation medium having non-polar surfaces which are substantially free from contamination with multivalent cations, and eluting the mixture of polynucleotides. The preferred surfaces are nonporous. The non-polar surfaces can be enclosed in a column. In the preferred embodiment, precautions are taken during the production of the medium so that it is substantially free of multivalent cation contaminants and the medium is treated, for example by an acid wash treatment and/or treatment with multivalent cation binding agent, to remove any residual surface metal contaminants. The preferred separation medium is characterized by having a DNA Separation Factor (defined hereinbelow) of at least 0.05. The preferred separation medium is also characterized by having a Mutation Separation Factor (as defined hereinbelow) of at least 0.1. In the preferred embodiment, the separation is made by Matched Ion Polynucleotide Chromatography (MIPC, as defined hereinbelow). Examples of non-polar surfaces include the surfaces of polymer beads and the surfaces of interstitial spaces within a polymeric monolith. The elution step preferably uses a mobile phase containing a counterion agent and a water-soluble organic solvent. Examples of a suitable organic solvent include alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures of one or more thereof, e.g., methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile. The most preferred organic solvent is acetonitrile. The counterion agent is preferably selected from the group consisting of lower alkyl primary amine, lower alkyl secondary amine, lower alkyl tertiary amine, lower trialkyammonium salt, quaternary ammonium salt, and mixtures of one or more thereof. Non-limiting examples of counterion agents include octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, or bromide. The most preferred counterion agent is triethylammonium acetate or triethylammonium hexafluoroisopropyl alcohol.
One embodiment of the invention provides a method for separating a mixture of polynucleotides, comprising applying a mixture of polynucleotides having up to 1500 base pairs to polymeric separation beads having non-polar surfaces which are substantially free from contamination with multivalent cations, and eluting said mixture of polynucleotides. In a particular embodiment of the separation medium, the invention provides a method for separating a mixture of polynucleotides comprising flowing a mixture of polynucleotides having up to 1500 base pairs through a separation column containing polymer beads which are substantially free from contamination with multivalent cations and having an average diameter of 0.5 to 100 microns, and separating the mixture of polynucleotides. The beads are preferably made from polymers, including mono- and di-vinyl substituted aromatic compounds such as styrene, substituted styrenes, alpha-substituted styrenes and divinylbenzene; acrylates and methacrylates; polyolefins such as polypropylene and polyethylene; polyesters; polyurethanes; polyamides; polycarbonates; and substituted polymers including fluorosubstituted ethylenes commonly known under the trademark TEFLON. The base polymer can also be mixtures of polymers, non-limiting examples of which include poly(styrene-divinylbenzene) and poly(ethylvinylbenzene-divinylbenzene). The polymer can be unsubstituted, or substituted with a hydrocarbon such as an alkyl group having from 1 to 1,000,000 carbons. In a preferred embodiment, the hydrocarbon is an alkyl group having from 1 to 24 carbons. In more preferred embodiment, the alkyl group has 1-8 carbons. The beads preferably have an average diameter of about 1-5 microns. In the preferred embodiment, precautions are taken during the production of the beads so that they are substantially free of multivalent cation contaminants and the beads are treated, for example by an acid wash treatment, to remove any residual surface metal contaminants. The beads of the invention are characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the beads are characterized by having a DNA Separation Factor of at least 0.5. Also in a preferred embodiment, the beads are characterized by having a Mutation Separation Factor of at least 0.1. The preferred method used in the separation is made by MIPC. In one embodiment, the beads are used in a capillary column to separate a mixture of polynucleotides by capillary electrochromatography. In other embodiments, the beads are used to separate the mixture by thin-layer chromatography or by high-speed thin-layer chromatography.
In addition to the beads (or other media) themselves being substantially metal-free, Applicants have also found that to achieve optimum peak separation the inner surfaces of the separation column (or other container) and all process solutions held within the column or flowing through the column are preferably substantially free of multivalent cation contaminants. This can be achieved by supplying and feeding solutions entering the separation column with components which have process solution-contacting surfaces made of material which does not release multivalent cations into the process solutions held within or flowing through the column, in order to protect the column from multivalent cation contamination. The process solution-contacting surfaces of the system components are preferably material selected from the group consisting of titanium, coated stainless steel, and organic polymer.
For additional protection, multivalent cations in mobile phase solutions and sample solutions entering the column can be removed by contacting these solutions with multivalent cation capture resin before the solutions enter the column to protect the separation medium from multivalent cation contamination. The multivalent capture resin is preferably cation exchange resin and/or chelating resin. The method of the present invention can be used to separate double stranded polynucleotides having up to about 1500 to 2000 base pairs. In many cases, the method is used to separate polynucleotides having up to 600 bases or base pairs, or which have up to 5 to 80 bases or base pairs. The mixture of polynucleotides can be a polymerase chain reaction product. The method preferably is performed at a temperature within the range of 20xc2x0 C. to 90xc2x0 C. The flow rate of mobile phase preferably is adjusted to yield a back-pressure not greater than 5000 psi. The method preferably employs an organic solvent that is water soluble. The method also preferably employs a counterion agent.
In another aspect, the present invention provides a polymeric bead having an average bead diameter of 0.5-100 micron. Precautions are taken during the production of the beads so that they are substantially free of multivalent cation contaminants and the beads are treated, for example by an acid wash treatment, to remove any residual surface metal contaminants. In one embodiment, the beads are characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the beads are characterized by having a DNA Separation Factor of at least 0.5. In a preferred embodiment, the beads are characterized by having a Mutation Separation Factor of at least 0.1. The bead preferably has an average diameter of about 1-10 microns, and most preferably has an average diameter of about 1-5 microns. The bead can be comprised of a copolymer of vinyl aromatic monomers. The vinyl aromatic monomers can be styrene, alkyl substituted styrene, alpha-methylstyrene or alkyl substituted alpha-methylstyrene. The bead can be a copolymer such as a copolymer of styrene, C1-6alkyl vinylbenzene and divinylbenzene. The bead can contain functional groups such as polyvinyl alcohol, hydroxy, nitro, halogen (e.g. bromo), cyano, aldehyde, or other groups that do not bind the sample. The bead can be unsubstituted or having bound thereto a hydrocarbon group having from 1 to 1,000,000 carbons. In one embodiment, the hydrocarbon group is an alkyl group having from 1 to 24 carbons. In another embodiment, the hydrocarbon group has from 1 to 8 carbons. In preferred embodiments, the bead is octadecyl modified poly(ethylvinylbenzene-divinylbenzene) or poly(styrene-divinylbenzene). The bead can also contain crosslinking-divinylmonomer such as divinyl benzene or butadiene.
In yet another embodiment, the invention is a method for separating a mixture of polynucleotides comprising flowing a mixture of polynucleotides having up to 1500 base pairs through a polymeric monolith, and separating the mixture of polynucleotides using MIPC. In this embodiment, the non-polar separation surfaces are the surfaces of interstitial spaces of a polymeric monolith. An example of such a monolith is a polymeric rod prepared within the confines of a chromatographic column. The monolith of the invention is characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the monolith is characterized by having a DNA Separation Factor of at least 0.5. The monolith is preferably characterized by having a Mutation Separation Factor of at least 0.1. The mobile phase used in the separation preferably includes an organic solvent as exemplified by alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures thereof. Examples of suitable solvents include methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile, and mixtures thereof. The most preferred organic solvent is acetonitrile. The mobile phase preferably includes a counterion agent such as lower primary, secondary and tertiary amines, and lower trialkyammonium salts, or quaternary ammonium salts. More specifically, the counterion agent can be octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, and bromide. However, the most preferred counterion agent is triethylammonium acetate.
In the preferred embodiment, precautions are taken during the production of the polymeric monolith so that it is substantially free of multivalent cation contaminants and the monolith is treated, for example, by an acid wash treatment, to remove any residual surface metal contaminants. In one embodiment, the monolith is characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the monolith is characterized by having a DNA Separation Factor of at least 0.5. Also in a preferred embodiment, the monolith is characterized by having a Mutation Separation Factor of at least 0.1.
In another aspect, the present invention is a method for treating the non-polar surface of a polymeric medium used for separating polynucleotides, such as the surface of beads in a MIPC column or the interstitial spaces in a polymeric monolith, in order to improve the resolution of polynucleotides, such as dsDNA, separated on said surface. This treatment includes contacting the surface with a solution containing a multivalent cation binding agent. In a preferred embodiment, the solution has a temperature of about 50xc2x0 C. to 90xc2x0 C. An example of this treatment includes flowing a solution containing a multivalent cation binding agent through a MIPC column, wherein the solution has a temperature of about 50xc2x0 C. to 90xc2x0 C. The preferred temperature is about 70xc2x0 C. to 80xc2x0 C. In a preferred embodiment, the multivalent cation binding agent is a coordination compound, examples of which include water-soluble chelating agents and crown ethers. Specific examples include acetylacetone, alizarin, aluminon, chloranilic acid, kojic acid, morin, rhodizonic acid, thionalide, thiourea, xcex1-furildioxime, nioxime, salicylaldoxime, dimethylglyoxime, xcex1-furildioxime, cupferron, xcex1-nitroso-xcex2-naphthol, nitroso-R-salt, diphenylthiocarbazone, diphenylcarbazone, eriochrome black T, PAN, SPADNS, glyoxal-bis(2-hydroxyanil), murexide, xcex1-benzoinoxime, mandelic acid, anthranilic acid, ethylenediamine, glycine, triaminotriethylamine, thionalide, triethylenetetramine, ethylenediaminetetraacetic acid (EDTA), metalphthalein, arsonic acids, xcex1,xcex1-bipyridine, 4-hydroxybenzothiazole, 8-hydroxyquinaldine, 8-hydroxyquinoline, 1,10-phenanthroline, picolinic acid, quinaldic acid, xcex1,xcex1xe2x80x2,xcex1xe2x80x3-terpyridyl, 9-methyl-2,3,7-trihydroxy-6-fluorone, pyrocatechol, salicylic acid, tiron, 4-chloro-1,2-dimercaptobenzene, dithiol, mercaptobenzothiazole, rubeanic acid, oxalic acid, sodium diethyldithiocarbarbamate, and zinc dibenzyldithiocarbamate. However, the most preferred chelating agent is EDTA. In this aspect of the invention, the solution preferably includes an organic solvent as exemplified by alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures thereof. Examples of suitable solvents include methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile, and mixtures thereof. The most preferred organic solvent is acetonitrile. In one embodiment, the solution can include a counterion agent such as lower primary, secondary and tertiary amines, and lower trialkyammonium salts, or quaternary ammonium salts. More specifically, the counterion agent can be octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, and bromide. However, the most preferred counterion agent is triethylammonium acetate.
In yet a further aspect, the invention provides a method for storing a medium used for separating polynucleotides, e.g., the beads of a MIPC column or a polymeric monolith, in order to improve the resolution of double stranded DNA fragments separated using the medium. In the case of a MIPC column, the preferred method includes flowing a solution containing a multivalent cation binding agent through the column prior to storing the column. In a preferred embodiment, the multivalent cation binding agent is a coordination compound, examples of which include water-soluble chelating agents and crown ethers. Specific examples include acetylacetone, alizarin, aluminon, chloranilic acid, kojic acid, morin, rhodizonic acid, thionalide, thiourea, xcex1-furildioxime, nioxime, salicylaldoxime, dimethylglyoxime, xcex1-furildioxime, cupferron, xcex1-nitroso-xcex2-naphthol, nitroso-R-salt, diphenylthiocarbazone, diphenylcarbazone, eriochrome black T, PAN, SPADNS, glyoxal-bis(2-hydroxyanil), murexide, xcex1-benzoinoxime, mandelic acid, anthranilic acid, ethylenediamine, glycine, triaminotriethylamine, thionalide, triethylenetetramine, EDTA, metalphthalein, arsonic acids, xcex1,xcex1xe2x80x2-bipyridine, 4-hydroxybenzothiazole, 8-hydroxyquinaldine, 8-hydroxyquinoline, 1,10-phenanthroline, picolinic acid, quinaldic acid, xcex1,xcex1xe2x80x2,xcex1xe2x80x3-terpyridyl, 9-methyl-2,3,7-trihydroxy-6-fluorone, pyrocatechol, salicylic acid, tiron, 4-chloro-1,2-dimercaptobenzene, dithiol, mercaptobenzothiazole, rubeanic acid, oxalic acid, sodium diethyldithiocarbarbamate, and zinc dibenzyldithiocarbamate. However, the most preferred chelating agent is EDTA. In this aspect of the invention, the solution preferably includes an organic solvent as exemplified by alcohols, nitrites, dimethylformamide, tetrahydrofuran, esters, and ethers. The most preferred organic solvent is acetonitrile. The solution can also include a counterion agent such as lower primary, secondary and tertiary amines, and lower trialkyammonium salts, or quaternary ammonium salts. More specifically, the counterion agent can be octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, and bromide. However, the most preferred counterion agent is triethylammonium acetate.